Evaporative cooling equipment such as cooling towers, evaporative condensers, and closed circuit fluid coolers are well known in the art. Such equipment has been used for many years to reject heat to the atmosphere. Cooling towers typically operate by distributing the water to be cooled over the top of a heat transfer surface and passing the water through the heat transfer surface while contacting the water with air. As a result of this contact, a portion of the water is evaporated into the air thereby cooling the remaining water.
In closed circuit fluid coolers and evaporative condensers, the fluid to be cooled, or the refrigerant to be condensed, is contained within a plurality of closed conduits. Cooling is accomplished by distributing cooling water over the outside of the conduits while at the same time contacting the cooling water with air.
In all applications of evaporative cooling equipment, proper water distribution within the equipment is critical to efficient performance of the equipment. Uneven distribution of water to the heat transfer surface will reduce the available air-to-water interfacial surface area which is necessary for heat transfer. Severe maldistribution of water may result in air flow being blocked through those areas of the heat transfer media which are flooded with water while at the same time causing air to bypass those areas of the media which are starved of water.
Generally, water distribution systems used in evaporative cooling equipment are either of the gravity feed type or the pressure spray distribution type. Gravity feed distribution system typically comprise a basin or pan which is positioned above the heat transfer media. In the bottom of the basin are positioned nozzles which operate to gravitationally pass water contained in the basin through the bottom of the basin while breaking up the water into smaller droplets and distributing the water droplets to the underlying heat transfer surface.
Pressure spray distribution systems, on the other hand, typically comprise multiple water distribution branches, or headers, positioned above the heat transfer with each branch containing a multitude of small spray nozzles. Generally, these nozzles are arranged closely in a uniform spacing in an attempt to achieve even water distribution across the typically rectangular top of the heat transfer surface. In the past, such nozzles generally had very small openings which easily became blocked by particles entrained in the water stream. In addition, the small nozzle opening restricted the flow through the nozzle which necessitated the use of many nozzles to sufficiently pass the required volume of water.
Attempts have been made, especially in the utilization of pressure spray distribution systems, to develop nozzles which will allow for the reduction of the number of nozzles required in any given system while at the same time achieving uniform water distribution. U.S. Pat. No. 4.058,262 describes one such spray distribution system in which there is shown use of spray nozzles wherein each nozzle forms with one adjacent nozzle a cooperative pair to create a generally rectangular spray pattern. Even though it is claimed that the number of nozzles is reduced with this spray distribution system, the nozzles shown in this patent are still of a generally small size and many would be needed in a large size cooling tower. In addition, the spray pattern generated by such system is generally not uniform.
U.S. Pat. No. 4,568,022 describes another spray distribution system utilizing nozzles which emit a generally circular spray pattern. Since the nozzles described in this patent emit spray about their entire 360.degree. perimeter, it is claimed that fewer nozzles are required. Also, this patent also describes that the sprays from one nozzle intersect with sprays from adjacent nozzles in both the length and width direction. However, the nozzles described are still of generally small size. In fact, the patent teaches that when such nozzles are used to distribute water over a cooling tower fill, such nozzles should be spaced about 8 inches apart on a given spray branch.
Although the spray distribution systems described above provide adequate water distribution in cooling towers of a relatively small to medium size, such distribution systems utilizing nozzles of a small size are not practical when used in large towers. In addition to the great number of small nozzles that would be required, even water distribution is difficult to achieve in towers of large size for several additional reasons.
In large towers, the problem of nozzle clogging is exacerbated due to the size of the tower components which allows even greater opportunity for foreign objects to find their way into the distribution system. To counteract this potential clogging problem, it is preferable on large towers to utilize nozzles with orifices as large as possible to allow them to pass most debris through the nozzle without becoming clogged. Of course, as is known in the art, the larger the nozzle orifice, the more difficult it is to achieve uniform water distribution.
Also, it is desired to keep the overall height of the evaporative cooling equipment to a minimum. This necessitates positioning the spray distribution system at a minimum distance above the top of the heat transfer surface. Unfortunately, the closer the distribution system is to the top of the heat transfer surface, the less room there is for the water to be distributed and the less surface area the spray from each nozzle is generally able to cover. This fact makes reducing the overall number of nozzles more difficult to achieve.
Additionally, in today's environment of energy consciousness, it is of critical importance to minimize the required spray water pumping pressure. Typically, pressure spray distribution systems have operated at spray pressures in the range of 3-8 psig. However, it is now desired to operate with spray pressures of no greater than 3 psig. This is especially true in very large towers where a very small increase in spray pressure required can add hundreds of thousands of dollars to the operating cost of the unit over its lifetime. Achieving uniform water distribution at low spray pressures is extremely difficult. This is due to the fact that at low spray pressures, there is very little energy available from the spray pressure to assist in spreading and distributing the water flow through the nozzles.
One method that could be used to distribute water in a large cooling tower would be to simply increase the size of the components of the distribution systems which have been successfully used on smaller towers. Unfortunately, such a simple solution will not result in uniform water distribution. If the size of a successful small distribution were increased, it would be necessary to increase all dimensions of the distribution system by a proportional amount. For example, if the nozzle opening had to be four times as large to be non-clogging, then all dimensions of the distribution system would have to be four times as great--including the height from the top of the heat transfer surface to the distribution system. Such an increase in tower height would be unacceptable.
Also, even the very good distribution system used on small towers have some areas of maldistribution. Generally these areas of maldistribution are small and do not significantly impact the performance of the tower. However, if the size of these small distribution systems were increased, the small areas of maldistribution which are acceptable on small towers will become proportionally larger and will become unacceptably large areas of maldistribution. Accordingly, it is necessary to utilize a completely different nozzle and distribution system design when providing a distribution system for a large cooling tower.
U.S. Pat. No. 4,208,359 describes a low head, non-clogging water distribution system that is intended to be used on large counterflow cooling towers. The nozzle described emits a generally hollow cone of water which is impacted upon a circular deflecting structure containing small, arcuate water-dispersing buttons. The resulting pattern produced by the nozzle is that of a full cone underneath the nozzle. The nozzle is sized to allow it to pass particles up to generally 1.5 inches in diameter. However, the fact that the nozzles of U.S. Pat. No. 4,208,359 emit a generally circular pattern limit the capability of this system to evenly distribute fluid to a rectangular area. Also, the spray cones emitted by adjacent nozzles do not interact with each other.